In March 2009, the Federal Communications Commission (FCC) introduced the Medical Device Radiocommunications Service (MedRadio) band in the range of 401-406 MHz which is a wireless communication regulation dedicated for biomedical telemetry. Formerly known as the 402-405 MHz Medical Implant Communication Service (MICS) band allocated in 1999, MedRadio is the superset of MICS in which additional adjacent bands at 401-402 MHz and 405-406 MHz are newly designated with twenty 100 kHz bandwidth channels to provide a total of five megahertz of contiguous spectrum and accommodate both implantable and wearable sensor devices for medical use.
Due to the need for reliable, continuous, and cost-effective health monitoring in hospitals and homes in recent years, both implantable and wearable sensors in Wireless Body Area Networks (WBAN) must meet ultra-low-power consumption for prolonged battery life. Since the wireless part of the sensor device usually consumes the most power, it is important to reduce both the current and the supply voltage of the transceiver to minimize the power consumption without compromising the performance.
Among several wireless bands for wearable sensor applications such as the industrial, scientific, and medical (ISM) frequencies at 433 MHz, 868-928 MHz, and 2.4 GHz respectively, some of these bands are not recognized globally while higher frequencies have the disadvantage of increased power consumption and free-space path loss. As higher frequencies are utilized for many other non-medical applications, it is prone to interference issues which are critical in biomedical applications where highly reliable communication is of key importance.
A low noise amplifier (LNA) usually dominates the total noise performance and sensitivity of a receiver used in biomedical applications. However, conventional LNAs typically have a limitation in performance improvement without increasing power, complexity or area.
FIG. 1a shows a conventional source degeneration cascode LNA (SDCLNA) 102. The SDCLNA 102 has a simple topology and can achieve a good noise performance with sufficient gain even at low bias current due to the passive amplification from the input matching circuitry. However, in order to constrain the current consumption of the SDCLNA 102 to less than 150 μA, the transistor Mn1 is biased close to threshold and its size is limited which leads to a small transconductance gm and a small gate-to-source capacitance Cgs. A small gm and Cgs will require large values of depletion capacitance Cd, gate inductance Lg, and source inductance Ls in order to match the impedance to 50Ω at 400 MHz. Thus, at a low frequency of operation (e.g. <1 GHz) and low power (<˜mW), large sizes of passive matching components (e.g. source inductor) are required for 50Ω matching. A small gm also leads to a limitation in the gain and noise performance. Thus, there is a limitation of performance improvement (noise and linearity) without power increase. It is difficult to further improve the noise figure (NF) of the SDCLNA 102 without increasing the power consumption.
FIG. 1b shows a conventional current-reuse LNA 104. The current-reuse LNA 104 has a current reuse topology and can provide an improved noise performance. However, the current-reuse LNA 104 requires additional DC feedback circuitry and additional passive components for performance improvement.